1. Field of the Invention
The present invention relates to an elevator safety device for causing a car to make an emergency stop when it has traveled above the top terminal landing or below the bottom terminal landing in the hoistway.
2. Description of the Related Art
In general, elevators are required to have a final limit switch which is a safety device. The final limit switch functions in accordance with Rule 209.3 Final Terminal Stopping Device in ASME A17.1-1990 described below.
That is, the device shall be so designed and installed that it will continue to function:
(1) at the top terminal landing, until the car has traveled above this landing a distance equal to the counterweight runby plus 1.5 times the buffer stroke, but in no case less than 2 it (610 mm); PA1 (2) at the bottom terminal landing, until the car rests on its fully compressed buffer.
FIG. 4 illustrates the construction of one example of a conventional elevator safety device. In the figure, a hoisting machine sheave 1 is provided in the upper portion of a hoistway, and a deflector sheave 2 is provided near this hoisting machine sheave 1. A rope 3 is wound around the sheave 1 and the deflector sheave 2. A car 4 hangs down from one end of the rope 3, while a counterweight 5 hangs down from the other end.
A car buffer 6A and a counterweight buffer 6B are each provided in the lowest portion of the hoistway. A car cam 9 serving as a car contactor is attached to the side surface of the car 4. Above the top terminal landing 7 of the hoistway, a plurality of top terminal landing final limit switches 10A (10A1 through 10An) are spaced apart and disposed along the hoisting direction. Below the bottom terminal landing of the hoistway, a plurality of bottom terminal landing final limit switches 11A (11A1 through 11An) are spaced apart and disposed along the hoisting direction. The top terminal landing and bottom terminal landing final limit switches 10A and 11A are engaged with the cam 9 for operation.
FIG. 5 is a control circuit diagram for the safety device of FIG. 4. Normally-closed contacts 10B1 through 10Bn of the top terminal landing final limit switches 10A1 through 10An and normally-closed contacts 11B1 through 11Bn of the bottom terminal landing final limit switches 11A through 11An are connected in series with one another between a positive main line P and a negative main line N of the direct-current power supply. Other safety devices 11 and a safety relay 12 are connected in series with the normally-closed contacts 10B1 through 10Bn and 11B1 through 11Bn.
Next, the operation will be described. When the elevator moves up, and for some reason cannot be stopped and travels above the top terminal landing 7, the car cam 9 engages with the top terminal landing final limit switch 10A1 to open the normally-closed contact 10B1. This deenergizes the safety relay 12, which stops power from being supplied to the hoisting machine and generates a braking command so that the car 4 makes an emergency stop. On the other hand, when the car 4 travels below the bottom terminal landing 8, the car cam 9 engages with the bottom terminal landing final limit switch 11A1 to open the normally-closed contact 11B1, thereby causing the car 4 to make an emergency stop in the same way.
When the operating speed of the elevator is low, the car buffer 6A stroke and the counterweight buffer 6B stroke, in general, are small. This means that even when the buffers 6A and 6B are full compressed after the car 4 or counterweight 5 has traveled above the top or below the bottom terminal landing and has stopped, the car cam 9 continues to be engaged with the top terminal landing final limit switch 10A1 or the bottom terminal landing final limit switch 11A1. Accordingly, in this case, only one final limit switch needs to be provided for the top terminal landing, and the bottom terminal landing respectively.
As the operating speed of the elevator increases, the stroke of each of the buffers 6A and 6B is increased in proportion to the square of the elevator speed. Therefore, when the buffers 6A and 6B are fully compressed, the car cam 9 passes the top terminal landing final limit switch 10A1 or the bottom terminal landing final limit switch 11A1, thereby causing either of the switches to be disengaged from the cam. To overcome this problem, a plurality of top and bottom terminal landing final limit switches 10A and 11A are respectively arranged, so that when the car 4 has traveled above the top terminal landing 7 or below the bottom terminal landing 8, the car cam 9 is continuously engaged with either of the switches to keep the safety relay 12 in a deenergized state.
When the car 4 has passed the top terminal landing 7 at a high speed, the counterweight 5 collides against the counterweight buffer 6B and stops. However, this is dangerous because the car 4 may be flung upward due to energy of motion. An action is taken to overcome this problem as described below. As mentioned above in Rule 209.3 in the ASME A17.1-1990, it is stated that the top terminal landing final limit switch should allow the safety device to continue to function at the top terminal landing, until the car has traveled above this landing a distance equal to the counterweight runby plus 1.5 times the buffer stroke, but in no case less than 2 ft (610 mm). Based on this, a plurality of top terminal landing final limit switches 10A are arranged so that they are not disengaged from the car cam 9 even when the car 4 has been flung upward.
In the conventional elevator safety device having the above-described construction, it is necessary to install a large number of top terminal landing final limit switches 10A1 through 10An to overcome the problem that the car 4 is flung upward. This results in increased costs.